This invention relates generally to silver alloys and more particularly to an improved silver alloy having a reduced porosity finish, and to an improved process of casting ornamental articles from such a silver alloy.
When casting articles, such as fine jewelry, it is important that the article being cast has a non-porous finish which is suitable for polishing. Along these lines, cast silver alloy articles having a reduced porosity finish also have a lower rejection rate than cast articles having a porous finish. Example 1 of the examples described below outlines the qualities and characteristics of a traditional silver/copper alloy (otherwise referred to as "sterling silver") in the areas of surface quality, structure quality and polishing capability. As discussed, while having a satisfactory structure quality and polishing capability, articles cast with this alloy tend to have an unsatisfactory surface quality with evidence of extreme porosity and microporosity occurring in articles sampled. The rejection rate of the articles associated with this prior art alloy is generally between ten and twenty percent which significantly increases the cost of the articles produced thereby lessening the manufacturer's ability to compete in the market place.
Reference should be made to the following U.S. Patents which disclose alloys in the same general field of the present invention: U.S. Pat. Nos. 2,157,933 (Hensel et al.); 2,161,253 (Hensel et al.): 4,030,918 (Sung et al.); 4,170,471 (Bailey); 4,409,181 (Coad); 4,883,745 (Mizuhara); 4,948,557 (Davitz); 4,980,243 (Malikowski et al.); 4,992,297 (van der Zel); and 5,021,214 (Sasaki et al.). Particular reference should be made to the patent to Coad which discloses, as one of its many embodiments, a brazing material consisting of from about 50% to about 99% by weight of a brazing alloy consisting of 25% to about 40% by weight of copper, from 0 to about 25% by weight indium, and the balance silver, and from about 1% to about 50% by weight of molybdenum. It will be shown that the silver alloy of the present invention differs significantly from Coad's brazing material in that it is silver-based and is suitable for casting fine silver jewelry having a substantially non-porous finish suitable for polishing.
The present invention has particular application to a silver alloy having a reduced porosity surface after it has been cast in a mold. Generally, the silver alloy consists of silver in a range from 92.50 to 99.00 percent by weight, indium in a range from 0.01 to 7.40 percent by weight, molybdenum in a range from 0.001 to 0.10 percent by weight, and the balance of copper. Preferably, the silver alloy consists of 93.50 percent by weight silver, 1.00 percent by weight indium, 0.05 percent by weight molybdenum, and the balance copper. Anti oxidants like zinc and silicon may also be added to the alloy to further reduce the porosity of the surface of the cast alloy.
A process for casting the silver alloy comprises the steps of: (a) providing a container suitable for melting and casting molten metal; (b) depositing in the container, elements of a silver alloy consisting of silver in a range from 92.50 to 99.00 percent by weight, indium in a range from 0.01 to 7.40 percent by weight, molybdenum in a range from 0.001 to 0.10 percent by weight, and the balance of copper; (c) heating the container to a temperature between 2600 to 2800 degrees Fahrenheit until the elements comprising the silver alloy substantially melt and are approximately at saturation level; (d) providing a mold; and (e) casting the melted silver alloy in the mold at a temperature around 2200 degrees Fahrenheit.
Accordingly, among the several objects of the present invention are the provision of an improved silver alloy having a reduced porosity finish; the provision of such an alloy which is suitable for polishing; the provision of such an alloy having increased strength characteristics; the provision of such an alloy which produces cast articles having a low rejection rate; and the provision of such an alloy which is strong, durable and suitable for mounting gems thereon.
Also among the several objects of the present invention are the process for casting the silver alloy capable of producing cast articles having a reduced porosity finish suitable for polishing; and the provision of such a process which produces cast articles having a low rejection rate.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds.